The invention refers to a wire electrode for the spark-erosive cutting of articles having an electrically conductive core and a jacket surrounding the core, which jacket comprises at least one α+β cover layer that contains β brass and/or β′ brass and α+β brass and/or or α+β′ brass.
The invention refers further to a method for the production of a wire electrode provided with a core outer layer from copper or α brass on which a zinc layer is deposited.
Such a wire electrode and method for production are known from EP 2 193 867 A 1. The wire electrode disclosed there is provided for the spark-erosive cutting of metallic work pieces. For processing, the wire electrode is subjected to a sufficiently high electric potential. On the other hand, the work piece normally is placed on ground potential. At the suitable proximity between the mechanically tensioned wire electrode and the work piece, a spark discharge occurs, thereby providing the desired cutting effect. Due to the spark discharge, material from the wire electrode is being constantly ablated from the wire. In order to prevent a complete wear-out of the wire electrode and thus tearing, during cutting or processing of the work piece, the wire is being continuously pulled through the cutting zone.
In order to improve the cutting performance of the wire electrode, EP 2 193 867 proposes to superpose several casing layers in radial direction, whereby the outer-most layer of the casing, which is directly facing the work piece, is made form a finely grained mixture of β brass and/or β′ brass, and in addition γ-brass. The γ-phase supposedly serves to increase the discharge action in the processing crack and would thus provide a high cutting quality. The γ-brass would have to be integrated suitably strong into the outer casing layer, in order to realize high cutting performances. Due to the fine grain feature of the phases, a great number of grain sizes should be present that preferably serve the spark discharge. This supposedly improves the ignition capacity of the wire and thus especially the quality of the cut. The thickness of the casing layer is normally dependent of the dimensioning of the article to be cut. As the outer layer containing β- and γ-brass, at a certain thickness, has a detrimental effect on the conductivity and the tensile strength of the wire electrode, according to EP 2 193 867 an inner casing is provided consisting of β- and/or β′-brass and/or α+β brass and/or α+β′ brass. The said phases are present next to each other in the inner casing layer as a coarse grained structure. Through this intermediate layer the total strength of the casing is increased and thus erosion resistance of the wire electrode raised.
From DE 199 11095 B4 a wire electrode is known that has a core of a copper/zinc alloy and a casing layer that envelops the core. The casing layer can be for example from brass, which is present in its α+β-phase.